It's pretty common to hear certain statements about health repeated so many times that it begins to gather a kind of "truthiness" - where the statement feels true, whether or not it is a fact. One of these is the "well-known fact" that red meat causes colon cancer. It's been studied quite a lot, and we hear it a lot, but what does the science tell us?Unfortunately, the science isn't always clear. In this case, many studies have been done on this - but the results are very mixed. You can point to studies that show a small correlation between colon/rectal cancer and red meat - and others which don't. Some studies have one type of flaw, and others have different flaws (there are very few "perfect studies".) So what are we to do in a case like this?
One thing is to look at research which attempts to summarize the work done in a specific area, such as the study in the July 2010 issue of Obesity Reviews, Red meat and colorectal cancer: a critical summary of prospective epidemiologic studies. The authors looked at 35 prospective studies (that means studies where they decide ahead of time what they are looking for, instead of looking backwards, which is often done but not as helpful), most of them quite large. What did they find?
Most of the results which showed a correlation between red meat and colon cancer only showed a weak one. And the studies and results tended to have some fairly major problems and inconsistencies:
- Lack of agreement on the definition of red meat (including whether or not processed meats like hot dogs and bacon were thrown in with steaks and burgers)
- The studies that showed an effect for red meat failed to show a "dose-response" effect - in other words, if red meat was a problem, you'd think that the more you eat, the more likely the cancer. Not true - for example, in one study a little meat showed a relationship with cancer, but a lot of meat showed none.
- The cooking method was seldom taken into account, even though it's known that high-temperature cooking of meat such as grilling and frying generates substances called heterocylic amines, which have been linked to cancer and diabetes.
- Most egregiously, factors which are known to correlate with eating red meat were often not taken into effect. People who eat a lot of red meat are more likely to be smokers, for example. They are also less likely to exercise, tend to eat less vegetables and fruits and tend to eat more sugar and refined carbohydrates. (Some studies have showed carbs to be related to colon cancer, others not.)
- Also, the meat in this studies was almost certainly not grass-fed, which might or might not make a difference.
Photo © Heiko Martin
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Have you ever read the China Study by Colin T Campbell? What do you think of those studies on animal protein?
I have followed a low carb/high protein diet for about two or so years now but am planning immediately drastically changing the sources or protein from meat poultry and fish to plant based protein after viewing
the following you tube video. If your watch this, you may as well.
http://www.youtube.com/watch?v=VIjanhKqVC4
Denney… I’m sorry, but to make such a drastic switch from animal based protein to plant based upon a youtube video is a bit extreme. Why not search out local organic farms that raise range/cage free chickens, grass-fed beef, wild caught fish and organic fruits & veggies?
And this work was funded by the Beef Checkoff, through the National Cattlemen’s Beef Association (NCBA), and by the Danish Agriculture & Food Council……….
no wonder why they came to such a different conclusion than all the previous systematic reviews and meta-analyses on the subject.
Tracy, on the China Study, I have not read it, but I’ve read some science-based analyses of it and it really seems to come up short, see:
http://www.sciencebasedmedicine.org/?p=385
http://rawfoodsos.com/2010/07/07/the-china-study-fact-or-fallac/
http://www.cholesterol-and-health.com/China-Study.html
http://www.cholesterol-and-health.com/Campbell-Masterjohn.html
Arne, I share your skepticism when it comes to studies funded by organizations which have a stake in the results. However, I have also learned that there is a difference between an organization commissioning a study and being a funding source. Some studies of low-carb eating, for example, would not have happened without the help of the Atkins Foundation. Researchers at major universities have applied to them for grants because they couldn’t get funding from anywhere else. But I also know that the Atkins foundation is absolutely meticulous when it comes to any input into the study itself – there is none, and they basically don’t hear anything until the results come out.
So while I keep funding sources in mind, I mostly try to answer the question, “is this study good science”. The study I wrote about is a) the most comprehensive meta-analysis I have found and b) actually didn’t come up with radically different results than other meta-analyses which generally show, as I said, very weak positive results. However, I think the points they made about confounding variables, and the other points as well, are really important. If beef consumption is correlated with refined carbohydrate consumption, we have to ask the question, “Was it the burger or the bun?” And that question has not been answered.